HARTFORD — A tweet sent Wednesday by Steve Perry, the principal of Capital Preparatory Magnet School, has caused a backlash and prompted the local teachers' union to ask the district and school board to investigate.

The only way to lose a fight is to stop fighting. All this did was piss me off. It's so on. Strap up, there will be head injuries.

Perry's message was posted after the city board of education declined late Tuesday to move forward with a controversial plan to turn over management of SAND Elementary School to Capital Preparatory Schools Inc., a nonprofit company run by Perry.

"The only way to lose a fight is to stop fighting," Perry wrote on his Twitter account. "All this did was piss me off. It's so on. Strap up, there will be head injuries." Perry's tweet prompted negative responses from dozens of Twitter users and critics such as blogger Jonathan Pelto.

In an email sent to Superintendent Christina Kishimoto and school board Chairman Matthew Poland, the teachers' union asked for the tweet to be investigated "immediately."

"From our perspective Steve Perry's comments were very threatening to all parties who opposed, especially those who voted to oppose, his plan for SAND and Capital Prep," wrote Andrea Johnson, president of the Hartford Federation of Teachers. "The Board of Education should not allow any of its employees to express violent actions towards others."

The Working Families Party also requested that the district take disciplinary action against Perry.

Hartford public schools spokesman David Medina said Thursday the district had no comment on Perry, and a call to Poland was not immediately returned.

Under the proposal, which SAND parents learned about only recently, Kishimoto sought permission to negotiate a memorandum of understanding with Perry's organization to begin managing SAND and Capital Prep Magnet School starting in 2014-15. The state requested the arrangement as part of a negotiated settlement with plaintiffs in the Sheff v. O'Neill desegregation case.

Perry, a public speaker and author who has frequently lambasted teachers' unions, said that the statement was "a metaphor about hard struggle" and called the ensuing controversy "troubling."

"There's no one mentioned, inferred or discussed at any point in the entire stream," he said. "This is simply an attempt by some people to take the focus off the very important issue at hand, which is to make sure Hartford … gets access to greater quality education by any means necessary.

"It's very, very sad to me that amidst all of the very, very real issues in education … someone's talking about my tweets," he said. "A metaphor. I could've said, 'It's going to be a bumpy ride.' I was being irreverent. It was a joke."

Perry said that the message was a general statement.

"It is not related to the vote," he said. "It is related to an ongoing fight for kids' rights."

Pelto said in an email Thursday evening that "to suggest that Steve Perry did not send his threatening tweet as a response to the Board of Education vote is absurd on its face."

Perry has sent out more than 31,000 tweets since he joined Twitter in August 2009 — about 20 per day — most of which are short musings on the state of education, advice for parents or expressions of frustration with the system.

"People who want to get what I represent, do. People who want to find fault, will," Perry said. "People know me. If I wanted to say something about somebody, I would have said something about somebody. I don't need to hide behind veiled things."

Perry has drawn criticism in the past for his multitasking — flying around the country for speaking engagements, writing books and appearing frequently on MSNBC and CNN and, recently, hosting the TV One reality show "Save My Son," all while leading the magnet school he founded in 2005.

Much of Perry's appeal as a speaker and commentator lies in his blunt criticism of teachers' unions and strong opinions about why schools are failing — another source of contention.

His anti-union stance and success — Capital Prep claims to send 100 percent of its graduates to four-year colleges, although Perry has acknowledged that not all of them can afford to attend — have resulted in veiled accusations from other educators of cherry-picking students and kicking out students who decide not to pursue a four-year degree.

In a 2011 profile on Perry, he told The Courant that the only requirement for acceptance at the school is "a pulse." But he acknowledged that families know from the start that the school's ultimate goal is to send students to college. He says he has "disenrolled" students, but never based on their college aspirations.